先化简,再求值:25x(0.4-y)2-10y(y-0.4)2,其中x=0.04,y=2.4.
问题描述:
先化简,再求值:25x(0.4-y)2-10y(y-0.4)2,其中x=0.04,y=2.4.
答
25x(0.4-y)2-10y(y-0.4)2,
=5(y-0.4)2(5x-2y),
当x=0.04,y=2.4时,
原式=5(2.4-0.4)2×(5×0.04-2×2.4)
=5×4×(-4.6)
=-92.